This invention relates generally to welding, and more particularly to methods for friction welding.
Friction welding of components such as gas turbine engine blades to rotors is known in the manufacture or repair of an integrally bladed disk, sometimes known as a BLISK. An integrally bladed disk is a disk or wheel on the periphery of which there is attached or carried a multiplicity of blades forming a monolithic structure or component. This same technique may also be used to attach a blade to a multi-stage monolithic drum rotor of a gas turbine engine. In a conventional rotor assembly, the blades are attached to a disk or wheel by interlocking dovetail attachment methods. In integrally bladed disks and drums the blades are either formed and machined integrally with the disk or drum or are welded or otherwise bonded thereto. The components to be bonded together are linearly or translationally rubbed one against the other with a reciprocating translational motion so that at their interface sufficient heat is generated by friction to effect the weld. Then, an axial welding force is applied to urge the components with a steady force to promote a better weld.
In the prior art, friction welding machine controls are tuned to prevent the weld from under or overshooting desired set points during conditioning, burn off, and forge phases of operation. While this tuning provides a uniform upset rate and predictable total upset during a weld, it can also restrict rate of application and amount of forge axial force. As a result, the horizontal displacement rate and compressive forces exerted by the machine can be reduced.
While prior art methods of friction welding work well when the same types of materials are used, testing has shown that some combinations of dissimilar alloys are prone to defects if insufficient displacement rate and/or compressive force are not applied when the oscillator movement is discontinued during the forge phase of the weld. Testing has also shown that frequency and amplitude of the oscillator during the conditioning and burn off phases, and the rate of oscillator decay during the forge phase, can impact upset rate during the forge phase, which can impact weld quality.